Project Summary- Project 1 Sleep apnea (SA) is a highly prevalent respiratory disease affecting several million people in the USA alone. Chronic Intermittent Hypoxia (CIH) is a hallmark manifestation of SA. Patients with SA, and rodents exposed to CIH exhibit elevated sympathetic nerve activity, which has been implicated in causing autonomic co- morbidities. The overall goal of the Project 1 is to delineate peripheral neural mechanisms underlying CIH- induced sympathetic activation and assess its impact on blood pressure. A heightened carotid body (CB) chemo reflex has been implicated as a major driver of CIH-induced sympathetic activation and gaseous messenger H2S mediates CB hyperactivity by CIH. Project 1 seeks to determine how H2S causes the CB activation by CIH. We test the hypothesis that H2S acting on olfactory receptor 78 (Olfr78) in glomus cells initiates a complex signaling cascade, involving a cAMP-dependent increase in [Ca2+]I leading to CB hyperactivity by CIH. We test this possibility using a combination of physiological, biochemical and molecular biological approaches on rats and mice exposed to CIH as well as in mice exhibiting spontaneous sleep apnea, and primary cultures of CB glomus cells. Studies in AIM 1 assess the role of Olfr78 in CB activation by CIH. AIM 2 determines whether CB activation by CIH requires cAMP activation by Olfr78 by H2S. AIM 3 determines how cAMP leads to CB activation by CIH. Experiments in AIM 4, determines the importance of CB H2S-Olfr78 signaling in CB excitation and sympathetic activation in mice exhibiting sleep apnea. Major conceptual and technical innovations include: a) H2S acting through odorant receptors mediates CIH-evoked CB excitation with profound consequences on autonomic functions is conceptually novel and has not been explored beyond the preliminary data presented in this application, b) assessing the significance of findings from experimental rodent model of CIH in mice exhibiting natural sleep apnea; and c) development of novel techniques to generate CB specific deletion of genes of interest. Project 1 has tight thematic linkages to Projects 2, 3, and 4 and utilizes Core B facilities for: a) exposing rats and mice to CIH, b) obtaining genetically engineered mice, c) targeted deletion of genes, and d) biochemical and molecular biological assays. Members of the investigative team have long-standing experience and expertise with the proposed approaches and a track record of working together as evidenced by joint publications. Successful completion of Project 1 is anticipated to establish a novel role for Olfr78 in mediating biological actions of H2S, which might lead to therapeutic strategies targeting of H2S-Olfr78 signaling to block CB reflex-dependent sympathetic hyperactivity.